ARSW, Adjective Rating Scale for Withdrawal; COWS, Clinical Opiate Withdrawal Scale; VAS, visual analog scale; M, male; F, female.
| Subjects | Behavioral measure | Sex differences |
| Human | Prevalence of heroin or prescription opioid use | M > F |
| F > M increased rate of heroin use | ||
| Rate of increased/decreased heroin or prescription opioid use across years (2007–2014) | F < M decreased rate of prescription opioid use (12) | |
| Human; heroin-dependent, in-patient setting | Self-reported craving and physiological measures after viewing: heroin-related imagery | F > M self-reported cravings and sadness, systolic blood pressure, heart rate |
| Heroin paraphernalia | F > M diastolic blood pressure, self-reported decreased joy | |
| M > F self-reported anger (14) | ||
| Human; opioid-dependent, buprenorphine tapering clinical trial | Self- and clinician-reported withdrawal symptoms (ARSW, COWS) and craving (VAS) | F > M withdrawal symptoms (ARSW, COWS) and subjective craving (VAS) (15) |
| Human; healthy volunteers | Self-reported drug effects questionnaire after intramuscular morphine administration | M > F self-reported positives effects and drug liking |
| F > M self-reported negative subjective effects (72) | ||
| Human; opioid-dependent, methadone- or buprenorphine-treated | Self-reported craving and mood using ecological momentary assessment | F > M self-reported craving for opioids as a function of stress severity |
| F > M self-reported craving for opioids in presence of stress and cues (73) | ||
| Human; opioid-dependent, morphine-stabilized, in opioid tapering clinical trial | COWS and self-reported withdrawal ratings after intramuscular naloxone injection | More F in high withdrawal phenotype than low |
| M = F in naloxone-precipitated withdrawal scores (78) | ||
| Mouse; 1 or 6 hours for intravenous heroin | Self-administration | F > M self-administered heroin |
| Somatic signs of withdrawal | F = M somatic withdrawal signs (22) | |
| Mouse; 1 or 12 hours for fentanyl vapor | Fentanyl intake during transition from short (1 hour) to long (12 hours) access | F > M intake in the first three sessions |
| Escalation across 10 days of 12-hour access | M > F change in intake (escalation slope) across days | |
| Naloxone-precipitated withdrawal | F > M somatic signs of withdrawal (23) | |
| Rat; 6-hour session for intravenous heroin | Days to acquisition criteria | F > M rate of acquisition (faster to acquire) |
| Infusions per session | F = M total intake during acquisition (83) | |
| Rat; 4-hour sessions for intravenous heroin | Infusions per session | F > M infusions at 1.25 or 3.75 μg per infusion |
| F = M infusions at 15–30 μg per infusion (84) | ||
| Rat; 1-hour session for oral oxycodone | Intake across doses | F > M mg/kg intake at 1.0 mg/ml |
| Naloxone-precipitated intake | F > M intake after naloxone injection | |
| Progressive ratio | F = M breakpoint | |
| Stress-primed reinstatement | F = M active lever presses (85) | |
| Rat; 2-hour session for intravenous fentanyl | Intake across doses | F > M infusions at 0.32–1 μg/kg dose |
| Motivation (demand curve) | F > M demand/essential value at 10 μg/kg per infusion (not 3.2 μg/kg per infusion) | |
| F = M baseline consumption (87) | ||
| Rat; 6-hour session for intravenous oxycodone | Buprenorphine effect on reinstatement | Buprenorphine reduced reinstatement in F but not in M |
| Buprenorphine effect on reacquisition of self-administration | Buprenorphine reduced reacquisition in F and M (89) | |
| Rat; 6-hour session for intravenous heroin | Incubation of heroin craving after forced abstinence | F and M incubated craving (increased responding) between abstinence days 1 and 21 |
| No incubation of craving between abstinence days 1 and 21 in F or M (88) | ||
| Mouse; 3-hour session for oral oxycodone | Intake across doses | F > M mg/kg intake at the 0.30–1 mg/kg dose |
| Cue-induced reinstatement | F = M (86) |